Apparatus for liquefying air and separating oxygen therefrom.



PATENTED NOV. 3, 1903.

- E. G. THRUPP. APPARATUS FOR LIQUEFYING AIR AND SEPARATING OXYGEN THEREFROM APPLICATION FILED MAY 18, 1901.

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- owing to its lower boiling-point,and this prop UNITED STATES.

Patented November 3, 1903;

PATENT OFFIGE.

APPARATUS FQR LIQUEFYING ME AND SEPARATING OXYGEN THEREFROM;

SPECIFICATION forming part of Letters Patent No. 743,349, dated November 3, 1903.

Application filed May 16. 1901.

and Separating Oxygen Therefrom; andI do hereby declare the following to be a f ull,c1ear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

It is well known that if air is liquefied and then allowed or caused to evaporate the nitrogen can be evaporated before the oxygen,

ertyof liquid air affords a means of separating the constituent gases of air more or less It is perfectly, according to circumstances. also well known that the amount of heat absorbed by the nitrogen and oxygen during.

evaporation and subsequent warming up to the normal temperature of the atmosphere is equal to that which must theoretically be abstracted from the same weight of fresh airin order to liquefy it.

- In practice it is impossible to realize a perfect interchange of temperature between the liquid air to be evaporated and the fresh supi as described in the specification of Letters Patent No. 642,505 of 1900, granted to me,

a and in the following description I refer to turbines as the expansion apparatus adopted. In any apparatus for the purposes named one of the important requirements is an effi able that the compressed air should enter the Serial No. 60,662. v (No model.)

turbine ata temperature as nearly as possible'equal to that of the liquid air produced or the temperature of the exhaust from the turbine, and to attain this condition it is necessary to employ pressures greater than the critical pressure of air and to employ some means of cooling the compressed air in addition to the ordinary temperature-interchanger, which cools the compressed air by a counter current of the gaseous part of the exhaust from the turbine, because the weight of the latter is less than that of the compressed air by the quantity of-liquid air produced. Any means of cooling applied to the compressed air before it enters the warm end of the interchanger can only be partially successful, and one part of myinvention consists in applying auxiliary cooling devices at the cold end of the interchanger, preferably by one or other of two methods or by a combination of both. One method consists in pump log back a portion of the liquid air into a pipe or receiver, through which thecompressed air passes on its way to the turbine, thus utilizing the latent heat of ebullition of the liquid to cool the compressed air which mixes with it. The cooling effect is thus produced without any material rise in temperature of the cooling agent, while the liquid evaporated is again passed through the liquefying-turbine and caused to do useful external work, which is greater than that required for pumping back the liquid. The other method consists in providing another turbine in which compressed air is expanded from such a pressure and temperature as will render its exhaust approximately at the temperature of liquid air without necessarily causing any liquefaction and mixing this exhaust air with that of the main or liquefying turbine in such proportions that the joint volumes shall be capable of cooling the supply of compressed air for the liquefying-turbine to the desired extent in the interchanger.

The foregoing devices are applicable not only to apparatus for separating oxygen from air, but also to apparatus for simply liquefying air.

For separating oxygen from the atmosphere the first stage of my process consists in liquefying air by means of a turbine and temperatureinterchanger, preferably utilizing the improvements hereinbefore described above for obtaining a high efficiency.

The liquid air is delivered into an evaporating vessel at about atmospheric pressure ready for treatment by the second stage. The evaporating vesselis provided with an outlet at the bottom for drawing 0% liquid oxygen and with an inlet or inlet-s for lowpressure gaseous air below the normal level of the surface of the liquid, and in the upper part of the vessel is an outlet for the air and evaporated nitrogen, communicating with the interchanger. A high-pressure receiver is placed in the upper part of the evaporating vessel or at the cold end of the interchanger, and it forms part of the compressed-air-supply circuit to the liquefying-turbine, the compressed air entering near the bottom and passing out at the top. During the first stage of the process the liquid for the auxiliary cooling of the compressed air is pumped intothis receiver, which is also fitted with an outletpipe in the lower part for drawing off liquid when its surface rises above a certain level. A trap may be employed to effect the regulation of this draining away of the liquid. on the same principle as the devices commonly used for draining water from steam-pipes, or it may be eifected at intervals by opening a valve by hand. The liquid so drained off passes into the evaporating vessel and mixes with the other liquid therein.

The second stage of the process (or condition of continuous working) consists in blowing air at a low pressure through the liquid in the evaporating vessel, having previously cooled the air nearly down to the temperature of the liquid in the interchanger. This causes the nitrogen to evaporate, and the latent heat of ebullition absorbed by the nitrogen is drawn from the air-blast, a portion of which is thereby liquefied,'and the liquid in the vessel tends to become more and more rich in oxygen. A continuous supply of fresh liquid air is necessary to make up for the evaporation of nitrogen, and this is derived partly from the liquefying-turbine and partly from the high-pressure receiver. The liquid oxygen is drawn off from the nitrogenevaporating vessel and pumped at high pressure into a coil or coils situated in the interchanger, which will act as a boilerand superheater for the oxygen, converting it into compressed gaseous Oxygen at a temperature approximately equal to that of the atmosphere, under which conditions it enters a turbine and is expanded down to a low pressure and temperature and delivered into the cold end of another coil in the interchanger, thus affording a second cooling effect before passing away to the gas-holder from which it is to be supplied for use.

The interchanger referred to above is a combination of coils and passages arranged to convey the following currents and counter currents:

' (A) Currents falling in temperature: First,

the compressed air supply to the high-pressure receiver and liquefying-turbine; second, the low-pressure air-blast delivering cold air to blow through the nitrogen evaporating vessel.

(B) Currents rising in temperature: First, the gaseous exhaust from the liqnefying-turbine mixed with the waste gases coming from the nitrogen-evaporating vessel; second, the high-pressure oxygen coming in the liquid state from the pump and going in the gaseous state to the second turbine; third, the low-pressure oxygen exhausted from the second turbine and going to the gas-holder.

When the apparatus is in full operation, the compressed-air supply (A 1) should be maintained at a pressure slightly below the critical pressure of air (which is about thirtynine atmospheres) in order to liquefy the air as much as possible in the coils and highpressure receiver.

The cooling agencies external to the interchanger consist of three turbines, namely: first, the air-liquefying turbine; second, the oxygen-expansion turbine; third, the auxiliary cooling-turbine. The last named is more important during the first stage of the operations when the evaporating vessel is being first charged with liquid air. Afterward, when the oxygen-turbine is in full operation, the third turbine is required less or not at all.

All the turbines are arranged to perform useful work by assisting to compress the air, to pump the liquid air and liquid oxygen, and to drive a blower for the low-pressure air-blast.

In order that my invention may be well understood, I'will describe it with reference to the accompanying drawing which illustrates an apparatus diagrammatically for the sake of simplicity and is not intended to show the relative proportions or exact situations of the parts or other details, which are obviously capable of many variations.

The fly-wheel of a high-pressure air-compressing engine is represented at A, and the steam-cylinder at B, and three air-compress ing cylinders operating step by step at G C 0 each having a delivery-pipe coil D D D immersed in a water-tank E, through which a current of cooling-water is passed, as indicated by the arrows 1 and 2. The coil D divides into two ways at F, one way leading to the suction of the third-stage compressingcylinder 0 and the other way leading to the auxiliary cooling-turbine G, either directly, as shown by dotted lines, or through a cooling-coil H, immersed in cold brine in a vessel H the said brine being supplied from any passes from I by the pipe 11 into the highpressure receiver K, situated in the upper part of the evaporating-chamber O,and thence passes by the pipe L to the liquefying-turbine M, which discharges liquefied air into the receiver N, and the liquid overflows through the passage 02 into the evaporating vessel 0. The gaseous portion of the exhaust from the turbine M also passes through the passage n and upward into the interchanger J, where it mixes with the exhaust from the auxiliary cooling-turbine G, and the combined volumes act as a medium for cooling the air in the coil I.

A pump P is provided to draw liquid from the receiver N through the suction-pipe p and force it through the delivery-pipe 19 into the high-pressure receiver K, which receiver K has an outlet communicating with a valve and trap 70 to draw off the liquid if it should rise above the outlet stand-pipe, which is in-v dicated on the drawing as projecting upward about half the height of the said receiver, while the com pressed-air-inlet pipet'enters below this level, so that the compressed air can bubble upward through the liquid and attain nearly the same temperature as that of the said liquid by the cooling eifect of the evaporation of the said liquid before the said compressed air passes to the liquefying-turbine M.

The liquid discharged through the passage 12 collects in the bottom of the evaporating vessel 0 until it rises through the pipe 0 high enough to overflow into the chamber 0 The said pipe 0 is open at the top and at the bottom to enable the liquid to How freely from the bottom of the chamber 0 into the charm ber 0 as indicated by the arrows in the drawing. When the liquid has accumulated up to the overflow-level, the low-pressure blower S, driven by the steam cylinder T, connected with the crank-shaft and fly-wheel U, is started and forces air through the cooling-coil R in the tank E and the coil R in the interchanger J into a pipe R communieating by an opening or openings or branch pipe or pipes into the lower part of the evaporatingchamber 0, so as to blow the low-pressure cold air through the liquid air, thereby evaporating chiefly liquid nitrogen and condensing a portion to a liquid from the lowpressure blast. The liquid in the chamber O is continually replenished by liquid air from the turbine M, and as the evaporation proceeds there is a continual evaporation of nitrogen and accumulation of liquid oxygen, which overflows through the pipe 0 into the chamber 0 A pump Q draws the liquid oxygen from the chamber 0 through the suctionpipe q and forces it at high pressure through the pipe g into the evaporating-coil V in the interchanger and thence by the pipe to to the third turbine W, which discharges into the low-pressure oxygen-coil X in the interchanger J. The oxygen assists in cooling the interchanger by evaporation in the coil V, and afterward its temperature is again reduced by expansion in the turbine W, and it further assists in cooling the interchanger as it passes through the coil XX, and it is finally delivered through the pipe Y to. the gas-holder or, other receiver ready for use.

The cross-hatched portions of the drawing represent non-conducting coverings. I prefer to construct the main interchangerJ with the four coils I, X, V, and R close together or arranged concentrically and to use a number of coils in parallel instead of single coils and to arrange the interchanger J with a central chamber and an outer concentric chamber or outer concentric chambers, through which the combined cold waste gases from the turbines G and M and the blast from the chamber 0 can pass successively before escaping and to arrange the four coils I, X, Y, and R also to pass successively through the concentric chamber or chambers. The drawing, however, shows the relative functions of the various coils and passages and also indicates how the turbines may be connected by speed-reduction gearing and belts to the airand highly-compressed air, and connections to discharge the gaseous portion of the exhaust from said expansion means into and through said inter-changer in the opposite direction to the current of high-pressure air to be cooled, in combination with an auxiliary turbine, connections supplying to the latter air at a lower pressure than the high-pressure air to be liquefied, and an exhaust from said auxiliary turbine connected to the interchanger at the same end of the latter as is the exhaust from the expansion means, as and for the purpose described.

2. Inair-liquefyingapparatus,air-compressing means, a cooler for the compressed air, a temperatu re-interchanger for further cooling the compressed air and means for expanding the compressed and cooled air, in combination with means for forcing a portion of the produced liquid air back into a pipe, or receiver, at the cold end of the said interchanger, to mix with and further cool, the compressed-air supply to the said expanding means, substantially as described. 3. Inair-liquefyingapparatus,air-compressing means, a cooler for the compressed air, a temperature-interchanger for further cooling the compressed air and means for expanding the compressed and cooled air, in combina- ICC tion with an auxiliary turbine actuated by compressed air to provide an augmented quan tity of cold exhaust gaseous air for cooling the compressed-air supply to the said expan ding means,'and with means of forcing a portion of the produced liquid air back into a pipe, or receiver, at the cold end of the said interchanger to mix with and further cool the compressed-air supply to the said expanding means, substantially as described.

4. In apparatus for separating oxygen from air, the combination with a high-pressure aircompressor, means for cooling the compressed air, a heat-interchanger, means for expanding the air, and a receptacle for collecting the liquid air, of a separate low-pressure air-compressor in connection with cooling means and a heat-interchanger, and a delivery from said compressor connected to the bottom portion of the liquid-air receptacle, whereby a blast of cold air is driven through and in direct contact with the liquid air, and means for withdrawing the oxygen thus obtained, substantially as specified.

5. In apparatus for separating oxygen from air, the combination of means for compressin g and cooling air, and a coil-containing temperature-interchanger for further cooling it, and means for driving a blast of cold gaseous air through the liquid air toevaporate chiefly the nitrogen from the liquid and condense a portion from the blast to a liquid and means for forcing liquid oxygen at high pressure into a coil in the ternperature-interchanger so as to evaporate oxygen therein and assist in cooling the fresh-air supplies, and a turbine in which the evaporated oxygen is subsequently expanded to lower its temperature again and further assist in cooling the fresh-air supplies by passing through another of the coils in the said interchanger, substantially as hereinbefore described.

In testimony whereof I affix my signature in presence of two witnesses.

EDGAR O. THRUPP.

\Vitnesses:

EDWD. GEO. DAVIES, T. TITUS GERALD. 

